Receiver arrangement



DEC- 19, 1957 w. A. SCHANBACHER 3,359,558

RECEIVER ARRANGEMENT Filed May 18, 1964 RADIO :REQ "I F j I T \G ls o 2I l 'TANK @Raw/Ib I I I PIRST AUDIO SECOND l E I ANTENNA DETECTOR FREQ.DETEcroR RELAY I 59 I STAGE TA6 AMD. `EIDQAMP DRIVER RELAY IF lf2 I ESTAGE STAGE STAGE I U I m IAQ I EN I SELF QUENCHING I SUPERIQEGENERATIVE I LE I CI NIO 24 E I 2 0 "/"T`T 1 7821 I 92 L I II I I H4I". Q6 I H2 I 76 I' Q4 IU- I )24 80 82 Sz C SIO O8 72 l I IZO L loi I 7-B I IOOI I I e {Ioq I I22 74 V 1 I==" ,691 I I IH6 l I @O I I 66 @I I ifI I I E I I Y z ugs 2 :Il ha .tb to I;

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fi?. j TIMEG RELAY A EJ; ENERGIzED 1 0 I O2 THRESI-Iow 5 B 09g VALUE oOID( ,E B Q D; RELAY NOT 2 5 C ENERGIzED 0: MIN TIME Q I SENSITIVITY gnbJD' VALUE INVENTOR, g 14,5 A IMM/AM A. Sc//A//:cf/f/e "0 CLTOFF BY 2-9i2/ 05 L VALUE f Af/5MG I TIME "'l ta t5 United States Patent 3,359,558RECEIVER ARRANGEMENT William A. Schanbacher, 7200 W. 90th St., LosAngeles, Calif. 90045 Filed May 18, 1964, Ser. No. 368,232 11 Claims.(Cl. 343-225) ABSTRACT OF THE DISCLOSURE There is described herein acommand receiver arrangement providing remote controlled actuation ofmechanisms upon receipt of a predetermined coded signal. The commandreceiver responds when the predetermined coded signal is present for apredetermined time period having a magnitude at least as great as apreselected value. The command receiver energizes a relay to control themechanism and for the condition of the relay energized, the gain of thecommand receiver is increased over the gain when the relay is notenergized so that the relay is and remains positively actuated eventhough the input signal decreased below the predetermined value as longas it is greater than a preselected cut-off value.

This invention relates to the receiver art and more particularly to animproved command receiver adapted to receive an audio frequencyamplitude modulated radio frequency signal and to energize a relay inresponse thereto for ultimate actuation of another mechanism.

In many remotely controlled applications, such as automatic garage dooropeners and the like, it has long been necessary to provide a low powerdrain, selectively tuned receiver that is stable in operation over awide range of ambient conditions and over comparatively long periods oftime. Such a receiver, generally termed a command receiver, is adaptedto receive a preselected coded signal and to positively initiateoperation of, for example, a garage door actuator mechanism, uponreceipt of such a coded signal, but not to operate the garage dooractuator mechanism when signals other than this properly preselectedcoded signal are present. Since many similar actuator mechanisms andtheir command receivers may be located in close geographic proximity, itis highly desirable that the tuning of such receivers be exceptionallyselective so that spurious operation of the garage door actuatormechanism does not occur when coded signals which may vary only slightlyfrom the preselected coded signal for a particular receiver are present.Also, the FCC requirements limiting the amount of re-radf'ation from-the command receiver must be complied with to avoid interference withother communications and with other similar command receivers.

It is preferred that such command receivers require onlya minimumoperating electrical power since they are generally in a stand-bycondition, ready to operate upon receipt of the preselected codedsignal. Further, it` has long been desirable to provide a thresholddetector and relay lock arrangement in such a command receiver so thatif the preselected coded signal is present for a predetermined timeinterval and is strong enough to initiate energizing a relay, the relaywill positively lock as long as the signal is present and Will notchatter, or sequentially open and close, at input signal levels at ornear the minimum input signal strength required for operation of thereceiver.

Coding of the transmitted signal that is sent lto the receiver isgenerally provided by audio-frequency amplitude modulation of radiofrequency signal. Thus, applicants improved receiver as described hereinis particularly useful when utilized in conjunction with the improvedtransmitter described in applicants copending patent application filedIan. 13, 1964, Ser. No. 337,354, now Patent No. 3,270,284 entitledTransmitter Arrangement. However, it will be appreciated that theimproved command receiver described herein may have many otherapplications and While, for purposes of illustration of the utility ofthe preferred embodiment of applicants invention, applicants improvedreceiver is described as embodied in a garage door opening andclosingarrangement, it will be appreciated that the invention herein isnot so limited.

Accordingly, it is an object of applicants invention to provide animproved command receiver.

It is another object of applicants invention to provide an improvedcommand receiver selectively tuned to initiate operation of an actuatormechanism upon receipt of only a preselected audio frequency amplitudemodulated radio frequency signal and having a very low amount ofre-radiation.

It is yet another object of applicants invention to provide an improvedcommand receiver that is highly stable over comparatively long periodsof time and throughout extreme variations in ambient conditions.

The above and other objects are achieved, according to one aspect ofapplicants invention, by providing, in a command receiver operating inthe range of 6 to 24 volts DC, an antenna adaptedr to receive atransmitted signal, which signal comprises an audio frequency amplitudemodulated radio frequency. A first detector stage is coupled to theantenna and the transmitted signal received thereby is coupled through atransformer into the first detector stage.

The first detector stage is adapted to establish a cyclical oscillatorycondition therein at a preselected radio frequency corresponding to theradio frequency in the transmitted signal by means of a cyclicalfrequency generating means which, in this embodiment of applicantsinvention, comprises a self-quenching super-regenerative circuit havinga squelch frequency rate on the order of thirty times the audiofrequency modulation frequency. The first detector stage includes meansfor adjusting the particular radio frequency of the oscillatory signal.Thus, a detected signal is provided resonant at the preselected radiofrequency and amplitude modulated by the preselected audio frequencyupon which is superimposed the squelch fre quency. v

The first detector stage also includes means for filtering both thepreselected resonant radio frequency of the signal and the squelchfrequency. The remaining detected audio frequency modulation of thesignal is coupled into an audio frequency amplification stage. Couplingof the detected audio frequency signal to the audio frequency amplifierstage is achieved through a gain control variable resistor thatestablishes the command sensitivity of the receiver. The audio frequencysignal is amplified in the audio frequency amplification stage throughan audio frequency tank circuit resonant at the preselected audiofrequency in the detected signal. This audio frequency tank circuitprovides the audio frequency selectivity of the receiver. Means areincluded in this audio frequency tank circuit for adjusting theparticular audio frequency at which the tank circuit is resonant so thatthe amplified detected audio frequency signal corresponds to the audiofrequency of the transmitted signal received by the antenna.

A second detector and DC amplifier stage is coupled to the audiofrequency amplication stage and receives the amplied audio frequencysignal and rectifies it to a DC control signal having a magnitudeproportional thereto. The second detector stage provides amplificationof the DC control signal to any predetermined value.

The amplified DC control signal is fed into a relay driver stage thatactuates a relay when the DC control signal has a magnitude equal to orgreater than a preselected threshold value. When the relay is soactuated by the DC control signal at a magnitude equal to or greaterthan the preselected threshold value, the gain of the first detectorstage is increased so that the relay will lock and stay locked until thestrength of the signal received by the antenna decreases to a valuesubstantially below that required to initially provide the thresholdvalue of the DC signal.

The receiver Vmay be powered by a conventional 115 to 120 voltalternating current power source or by a DC power source. In eitherevent the receiver power input is provided with suitable filtering ofany -radio frequency in the input signal as well as smoothing out anyripples in the input power. Further, if conventional alternating currentpower is utilized, means are incorporated to rectify the input power sothat the receiver is powered by DC in the range of 6 to 24 volts.

The above and other objects are more fully described inthe followingdetailed description taken together with the accompanying drawingwherein similar reference characters refer to similar elementsthroughout and in which:

FIGURE 1 is a block diagram of one embodiment of applicants invention;

FIGURE 2 is a schematic diagram thereof;

FIGURES 3, 4 and 5 are graphical illustrations of the relationshipbetween various parameters in one embodiment of applicants improvedcommand receiver.

Referring now to FIGURE 1, there is shown a block diagram for thevarious stages comprising applicants improved command receiver,generally designated 10. When applicants improved receiver is utilized,for example, in a remotely controlled garage door opening and closingarrangement, the actuator for moving the garage door is not part of thereceiver itself, but is merely controlled through a relay by thereceiver 10. Thus, the receiver 10 has as its basic purpose the functionof energizing the relay upon receipt of a preselected coded signal. Therelay may be utilized to control, through appropriate circuitry, manydevices other than garage door actuators. However, for purposes ofillustration, applicants improved command receiver 10 is describedherein as utilized in such a garage door opening application.

,The command receiver 10 comprises an antenna stage 12 adapted toreceive a transmitted signal, which signal comprises an audio frequencyamplitude modulated radio frequency signal in which both the frequencyof the radio frequency signal and the frequency of the audio frequencyamplitude modulation are preselected so that the receiver 10 energizes arelay, as described below, only when both the preselected radiofrequency and the preselected audio frequency are in the transmittedsignal and the signal is present at the antenna 12 for a predeterminedtime at or above a predetermined strength. The antenna receives such atransmitted signal and couples the signal into a first detector stage 14coupled thereto.

As described below in detail, the first detector stage 14 comprises acyclical frequency generating means which, in this embodiment ofapplicants invention, comprises a self-quenching super-regenerativedetector 14a: that cyclically oscillates at the preselected radiofrequency, corresponding to the radio frequency in the transmittedsignal received by the antenna 12, for which a radio frequency tankcircuit 14b is selectively tuned. The amplitude of the oscillatorysignal generated by the self-quenching super-regenerative detector 14aat the preselected radio frequency builds up in strength until it wouldbe selfsustaining in the radio frequency tank circuit 14h, but at thispoint the gain of the self-quenching super-regenerative detector 14a isdecreased and the oscillation dies. The basic cyclic frequency, that is,the squelch frequency, of the self-quenching super-regenerative detector14a is selected to be, in the absence of a transmitted signal, forexample, on the order of 2 to 50 times the frequency of the preselectedaudio frequency amplitude modulation of the transmitted signal receivedby the antenna 12.

When the proper transmitted signal is received by the antenna 12, it iscoupled into the radio frequency tank circuit 14b and this increases thesquelch frequency rate of the self-quenching super-regenerative detectorstage 14a.

The increase in the squelch frequency rate is a function of the strengthof the transmitted signal received by the antenna stage 12 which, ofcourse, cyclically varies at the preselected audio frequency modulationrate. The oscillating period at the preselected radio frequency in thefirst detector stage 14 is constant and the average on time, that is theaverage time over a number of cycles during which an oscillation at thepreselected radio frequency is present, and consequently the averagecurrent drawn by the self-generating super-regenerative detector 14avaries at the preselected audio frequency rate. This variation inaverage current drain at the preselected audio frequency rate providesthe detected audio frequency signal utilized for operation of thecommand receiver 10.

The first detector stage 14 also includes filtering means for filteringboth the preselected radio frequency component and the self-quenchingfrequency component of the signal therein, and for coupling the detectedpreselected audio frequency signal into an audio frequency amplifierstage 16. The audio frequency lamplifier stage 16 includes an audiofrequency tank circ-uit selectively tuned for a resonant frequency atthe preselected ya-udio frequency of the transmitted signal. Thus, whenthe transmitted signal received by the antenna 12 has this preselectedaudio frequency amplitude modulation component, the audio frequencyamplifier stage 16 amplifies the detected audio frequency signal coupledthereto from the first detector stage 14 and feeds this amplified audiofrequency signal into a second detector and DC amplifier stage 18.

The second detector and DC amplifier stage 18 rectiies the amplifieddetected audio frequency signal to a DC signal and ampliiies the DCsignal to provide .an amplified DC control signal having a magnitudeproportional to the logarithm of the strength of the transmitted signalas received by the antenna 12.

This amplified DC control signal is fed into a relay driver stage 20 toenergize a rel-ay 22 when the magnitude of the amplified DC controlsignal is greater than a first predetermined value called the thresholdvalue, and the detected audio frequency signal is present for asufficient time to `provide this amplified DC control signal at or abovethe threshold value..

The relay driver stage 20 also includes, as described below, means forlocking in the relay 22 once it has been energized and holding the relay22 locked in even though the strength of the transmitted signal receivedby the antenna 12 decreases below the minimum sensitivity value requiredto provide the DC cont-rol signal of the threshold value. Therefore,once the relay 22 is energized, it stays energized even though thesignal strength of the transmitted signal received by the antenna 12decreases below the minimum sensitivity value for as long .a time periodas the strength of the transmitted signal remains above a cut-off valuethat is lower than the minimum sensitivity value by Ia predeterminedamount. Thus, there is no chatter of the relay 22 once it has originallybeen energized and -continuous energization of the relay 22 down to anydesired lower level of strength of the transmitted signal received bythe .antenna 12 may be provided. Means areprovided so that the cyclicvariation in the transmitted signal strength due to the audio frequencymodulation do not effect the magnitude of the DC control signa When therelay 22 is energized, an information signal is sent, throughappropriate circuitry, to an actuator mechanism 24 for operation of, forexample, opening and closing garage doors. The actuator mechanism 24 andcircuitry associated therewith do not form a part of applicantsinvention herein.

Referring now to FIGURE 2, there is shown a schematic diagram of thepreferred embodiment of applieants invention of an improved commandreceiver 10. It will be appreciated that the particular valuesdesignated for the various components of the receiver illustrated byschematic diagram in FIGURE 2 is for illustrative purposes only andapplicants invention is not so limited to cornponents having the same orequivalent values.

The antenna stage 12 comprises a receiving7 antenna 26 which, forexample, may comprise a short length, on the order of seven inches, ofNo. 12 copper wire leading into a primary winding 28 of a radiofrequency transformer 30. The receiving Iantenna. 26 is shunted byresistor 32 which, for example, may be on the order of 47 ohms, and thisresistor 32 is a load terminating impedance of the receiving antenna 26to provide a high frequency stability and, ,as described below, alsotends to eliminate even the small amount of re-radiation of theoscillatory signal generated in the first ldetector stage 14 from thereceiving antenna 26. The `other end of the primary winding 2S of theradio frequency transformer 30 provides the ground connection 34 to thecommand receiver 10 ground bus 35.

The first detector stage 14 has the radio frequency tank circuit 14bcoupled to the antenna stage 12 by the secondary winding 38 of the radiofrequency transformer 30. The secondary winding 38 of the radiofrequency transformer 30 and a variable capacitor 40 comprise the radiofrequency tank circuit 14b. The resonant frequency of the radiofrequency tank circuit 14b is preselected by adjustment of the variablecapacitor 40 so that it is selectively tuned to :and resonant at theparticular preselected radio frequency corresponding to the radiofrequency in the transmitted signal received by the receiving antenna 26for lwhich operation of the receiver 10 is desired.

A signal at the predetermined radio frequency is cyclically supplied inthe radio frequency tank circuit 14b by the self-quenchingsuper-regenerative detector 14a comprising triode 42, resistor 44 andcapacitor 46, yas well as inductor S8, resistor 56 and capacitor 62. Thetriode 42 may, for example, comprise a Nuvistor such as RadioCorporation of America Nuvistor No. 7586 having a transcond-uctance onthe order of 4000 micromhos at an operating plate voltage ofapproximately 12 volts. The triode 42 has a plate 48, a cathode S0,cathode heater 52 and grid 54. The grid 54 bias voltage of the triode42, that is, the voltage difference between the grid 54 and the cathode50, regulates the gain of the triode 42 and is controlled so that theradio frequency signal supplied to the radio frequency tank circuit 14bsequentially passes through a voltage range wherein oscillation will besequentially supported and non-supported at the preselected radiofrequency therein. This is illustrated in the curve of FIGURE 3 whichshows the variation in the grid voltage (Eg) lof the triode 42 withtime. At time ta when the grid 54 voltage is negative with respect tothe cathode 50, resistor 44 and capacitor 46 provide a specificdischarge time constant, for example, on the order of 1.5 l0h6seconds:;0.75 106 seconds, and as the grid voltage becomes more positive(less negative with respect to the cathode 50) it reaches a value attime tb when sufficient gain through the triode 42 is obtained. As thisgain increases, the oscillation at the preselected radio frequencyincreases in magnitude and a time te the grid 54 voltage, as theoscillation builds up in value, becomes positive. At this time tc, thatis, when the grid 54 voltage becomes positive with respect to thecathode 50, there is a discharge across capacitor 46 and the grid 54voltage then becomes negative and the oscillation dies and the grid 54voltage once again becomes negative with respect to the cathode 50, asshown at time la. This cycle then repeats, in the absence of an inputfrom the antenna 12 of a signal at the preselected radio frequency, atthe selfquenching frequency provided by the discharge time constant ofresistor 44, capacitor 46 and the gain characteristics of triode 42.Operation of the receiver 10 in the presence of such a signal isdescribed below.

The combination of capacitor 46 and resistor 44 also provides theprimary gain'control of the first detector stage 14.

While a resonant signal at the preselected radio frequency is thuscyclically generated in the radio frequency tank circuit 14b and isre-radiated out the receiving antenna 26 being supplied thereto by radiofrequency transformer 30, applicant has found that the very lowoperating power, that is, on the order of 0.1 milliwatt, together withthe values of the components utilized herein, provide that there-radiated signal does not affect operation of adjacent devices of asimilar design and substantially eliminates emanation of radio frequencyinterference noises. Thus, applicants improved command receiver 10allows elimination of shielding or other re-radiation protective devicescommonly utilized in prior art, super-regenerative command receivers.

The receiver 10 is always maintained in a stand-by condition in whichthe above-described resonant signal at the preselected radio frequencyis cyclically supplied in the radio frequency tank circuit 14b throughthe action of the self-quenching super-regenerative detector 14a. Theself-quenching frequency of the regenerative signal, that is,corresponding to the time interval from ta to ra in FIGURE 3, may beselected to be on the order of two to fifty times the frequency of thepreselected audio frequency modulation signal component that is expectedto be present in the transmitted signal received by the receivingantenna 26.

In attempting to meet the above-described re-radiation limitations ithas long been the practice in the command receiver art to include atleast one isolation stage comprising,`for example, a triode similar totriode 42 interposed between the antenna stage 12 and the rst detectorstage 14. However, applicant has found that by providing an operatingvoltage to the command receiver 10 in the range of 6 to 2.4 volts DCwith a plate 48 to cathode 50, voltage on the order of 12 volts DC, alllimitations on re-radiation are met without any shielding stage or otherre-radiation shielding arrangement. This operating voltage range alsopermits applicant to utilize transistors in the command receiver 10 sothat power consumption thereof is low and reliability is high.

When the receiving antenna 26 receives a transmitted signal having theselected radio frequency amplitude modulated by the preselected audiofrequency it is coupled into the radio frequency tank circuit 14b eventhough the grid 54 bias voltage of the triode 42 is less than thatnecessary to support such an oscillation in the absence of thetransmitted signal. Thus, the average oscillation on time over a numberof cycles is increased above that obtained in the `absence of atransmitted signal at the preselected radio frequency received by thereceiving antenna 26, and this increase in the average on time thatoscillation at the preselected radio frequency is present in the radiofrequency tank circuit 14b provides the detected preselected audiofrequency modulation signal, which, as described below, provides desiredoperation of the command receiver 10 to act-uate a relay. When thereceiving antenna 26 so receives a transmitted signal having thepreselected audio frequency amplitude modulation of the preselectedradio frequency, oscillation is supported at shorter time intervals, atthe preselected radio frequency, in the radio frequency tank circuit14b.

Resistor 56 and inductor v58 provide a controlled load to the signal inthe first detector stage 14'together with resistor 32 and the primarywinding 28 of the radio frequency transformer 30. The inductor 58 alsoprovides an inductive impedance and is an audio by-pass to the detectedaudio frequency signal for the rst detector stage 14 output. Theinductor 58 compensates for electron transit time in the triode 42 sothat phase lag of the triode 42 does not cause operation of the radiofrequency tank circuit 14b at frequencies other than the preselectedradio frequency. Applicant has found that vin utilizing theabovedescribed 6 to 24 volt DC' operating voltage, compensation for theelectron transit time provided, primarily, by the inductor 58substantially eliminates any tendency towards spurious operation andsignal drift induced by minor variations of operating voltage.

Variable resistor 60 and capacitor 62 provide filtering of the squelchfrequency component of the signal in the radio frequency tank circuit14b that is superimpressed on the signal therein. The variable resistor60 also controls the basic sensitivity of the command receiver and bysuitably adjusting the resistor 60, the predetermined value of thesignal strength of the transmitted signal, that is, the minimumsensitivity value to result in the DC control signal at the thresholdvalue, received by the antenna 26 that will allow ultimate operation ofthe relay 22 is adjusted. Inductor 58, resistor 56, variable resistor 60and capacitor 62 also `filter out the radio frequency component of thesignal to allow transmission of the detected audio frequency modulationsignal into the audio frequency amplifying stage 16.

When the command receiver 10 is utilized in conjunction with thetransmitter described in the copending patent application of applicantmentioned above, applicant has found that the following values for thecomponents provide satisfactory operation of the first detector stage14: capacitor 46, 100 picofaradsiSO picofarads; capacitor 40, variablebetween 1.5 and 9 picofarads; capacitor 62, 1800 picofarads; inductor58, .82 microhenry, resistor 60, variable between zero and 5,000 ohms.The preselected radio frequency is preferably within the range of 250 to300 megacycles and the preselected audio frequency is preferably withinthe range of 12 to 24 kilocycles.

As noted above, the rst detector stage 14 includes means for filteringthe resonant signal in the radio -frequency tank circuit 14b to removeboth the radio frequency component and the regenerative frequencycomponent therefrom to leave, substantially, the detected audiofrequency signal to be coupled into the audio frequency amplifier stage16.

FIGURE 4 illustrates the wave forms associated with the signaltransmitted through the command receiver 10 at various points therof.Curve A of FIGURE 4 illustrates the Wave form as obtained at point A,that is, `at the input to the variable resistor 60. As shown, the radiofrequency component has been substantially filtered out and the signalcomprises the detected audio frequency signal upon which is superimposdthe attenuatd squelch frequency. This is the detected audio frequncysignal that is fed into the audio frequency amplifier 16. An audiofrequency tank circuit 64 comprising variable inductor 66, into which istapped the detected audio frequency signal, and capacitor 69 is providedin the audio frequency amplifier stage 16. The .audio frequency tankcircuit 64 is resonant for the preselected audio frequency that isexpected to be in the transmitted signal received by the receivingantenna 26 and is adjusted therefor by suitably adjusting variableinductor 66. The variable inductor 66 may be conveniently described asan audio coil and upon proper adjustment thereof the audio frequencytank circuit 64 is resonant only for the preselected audio frequency.

Transistor 68 having base electrode 70, emitter electrode 72 andcollector electrode 74 receives the audio frequency signal at its baseelectrode 70 from the variable resistor 60 and the collector electrode74 is tapped into the variable inductor 66 to feed the detected audiofrequency signal therein without significantly decreasing theselectivity of tank circuit 64. The transistor 68 is a modulationamplifier transistor of the P-N-P type and, for example, may be a RadioCorporation of America number 2N414. Resistor 76 provides both a bias onthe audio frequency modulation amplifier transistor 68, as well ascontributing to the gain control for the audio amplifier stage' 16.Filter capacitor 78 together with resistor 80 provide a high voltagegain through transistor 68 g. to the audio frequency tank circuit 64 andresistor 80 controls the current bias for the transistor 68.

The signal at the base electrode 70 of the transistor 68 has only aslight ripple at the regenerative signal frequency superimposed upon thedetected audio frequency signal. When the preselected audio frequency ispresent to establish the resonant condition in the audio frequency tankcircuit 64, filtering is virtually completed and at point B the signalis substantially a smooth sine Wave at the detected audio frequencymodulation frequency as illustrated by curve B in FIGURE 4.

This detected audio frequency sine Wave is fed into the second detectorstage 18 at the base electrode 82 of a DC amplifier transistor 84 havingan emitter electrode 86 and a collector electrode 88. The DC amplifiertransistor 84 rectifies the audio frequency signal and provides a DCsteady state control signal having a magnitude proportional to thelogarithm of the magnitude of the audio frequency modulation signal inthe transmitted signal received by the receiving antenna 26. Thus, theDC amplifier transistor 84 which, for example, may be a Texas instrument2N388 NPN type transistor, acts as -an impedance multiplier at the baseelectrode 82 thereof, for resistor 90 connected to the emitter electrode86 thereof. The amplification is controlled by the ratio of the sum ofthe resistance values of resistors 92 and 94 divided by the value of theresistance of the resistor 90.

Thus, applicant has found that DC amplification is provided 4to result,in `a DC control lsignal at a preselected magnitude and the preselectedmagnitude is proportional to the logarithm of the signal strength of theaudio frequency amplitude modulation component of the transmitted signalreceived by the receiving antenna 26.

Capacitor 96 provides noise filtering in combination with resistors 92,94 and 98 and filters against spurious operation of the receiver 10 dueto noise at the receiver by having a comparatively long time constant.Thus, presence of a transmitted signal at the receiver antenna 26 at apredetermined strength and having the preselected radio frequencyamplitude modulated by the preselected audio frequency for a sufficientlong period of time, for example 0.5 second, provides the desiredcombination of parameters necessary for operation of the commandreceiver 10. This time delay also provides that the DC control signal besubstantially steady state and independent of the cyclic strengthvariations of the transmitted signal due to the audio frequencyamplitude modulation.

Resistor 92 is a thermistor, such as Fenwal No. KAS 3i 1 having anominal value of 3000 ohms at 25 C. and provides temperaturecompensation for the audio frequency amplification stage 16 and seconddetector 18 stage over comparatively wide ranges of temperature to allowa substantially constant gain in the receiver 10. The resistor 98 isessentially a coupling resistor and couples the amplified DC controlsignal, as it appears at point C and as: sh'own in curve C on FIGURE 4,into the relay driver stage 20.

This signal is fed into relay driver stage 20 through the base electrode100 of a relay driver transistor 102 which, for example, may be a RadioCorporation of America No. 2N414 P-N-P type transistor and the collectorelectrode 104 thereof is coupled to the relay 22. The emitter electrode106 of the relay driver transistor 102 is coupled to the emitterelectrode 108 of an impedance divider transistor 110. The impedancedivider transistor has a base electrode 112 and a collector electrode114. Impedance divider transistor 110 provides a very small currentdrain in the command receiver 10 during both stand-by operation andrelay actuation. The impedance divider transistor 110 divides theimpedance provided by resistors 116 and 118 and establishes thethreshold voltage level for conduction in the relay driver transistor102.

When the magnitude of the DC control signal supplied to the baseelectrode of the relay driver transistor 102 exceeds this thresholdvalue, for example 3 v'olts as established at the emitter electrode 106thereof by the impedance divider transistor 110, the relay drivertransistor 102 commences to conduct and cnergizes the relay 22 connectedto the collector electrode 104 thereof. This threshold value at whichthe relay driver transistor 102 commences to conduct is controlled bythe resistors 116 and 118 in conjunction with the impedance dividertransistor 110.

Once the relay driver transistor 102 commences to conduct and the relay22 is energized, the plate voltage on the triode 42 is decreased due tothe increased load on the power supply (not shown), thereby increasingthe gain in the circuit of the command receiver so that the magnitude ofthe DC signal applied to the base electrode 100 of the relay drivertransistor 102 increases abruptly to hold the relay 22 in the energizedposition, for a given transmitted signal strength. That is, if the inputsignal received by the receiving antenna 26 is strong enough to commenceoperation and energize the relay 22,

that is, at the minimum sensitivity value, once the relay 22 is closedit will stay closed, because of the increase in the gain of the receiver10 for the same transmitted signal strength, until the transmittedsignal strength drops below a predetermined value termed the cut-offvalue. The cut-off value of the input signal strength corresponds tothat value of input signal strength that produces an amplified DCcontrol signal at the relay driver transistor 102 having a magnitudejust at the threshold value When the relay 22 is energized. Thus, oncethe strength of the transmitted signal received by the antenna 12 dropsbelow the cut-off value, the magnitude of the DC control signal suppliedto the relay driver transistor 102 decreases tbelow the threshold valueand the relay 22 is deenergized. This results in an abrupt decrease inthe magnitude of the DC signal, since the gain of the command receiver10 is suddenly decreased. Therefore, once the transmitted signalreceived `by the antenna 12 reaches the minimum sensitivity value toprovide a DC control signal to the relay driver transistor 102 at thethreshold value and the relay 22 is thereby energized, the relay 22remains energized even though the transmitted signal strength decreasesbelow the minimum sensitivity value as long as it stays above thecut-off value. This substantially eliminates chatter and sequentialopening and closing of the relay 22.

The relationship ybetween the transmitted signal strength as received'by the receiving antenna 26 land the DC control signal magnitudesupplied to the relay driver transistor 102 is illustrated on FIGURE 5.As shown on FIGURE 5, and with reference to FIGURE 2, curve A representsthe strength of the transmitted signal received by the receiving antenna26 and curve B represents the magnitude of the DC control signalsupplied to the base electrode 100 of the relay driver transistor 102.As noted above, the magnitude of the DC control signal is proportionalto the logarithm of the transmitted signal strength.

Until time t1 the transmitted signal strength is less than the minimumsensitivity value, which value is adjusted by variable resistor 60. TheDC control signal magnitude is similarly less than the threshold valuefor conduction of the relay driver transistor 102 as determined byimpedance divider transistor 110. At time t1, when the transmittedsignal strength reaches the minimum sensitivity value, the DC controlsignal magnitude reaches the threshold value land the relay 22 isenergized. When the relay 22 is energized, there is a sudden increase inthe gain of the command receiver 10 and this results in an abruptincrease in the magnitude of the DC control signal, as

yshown by por-tion B1 of curve B. For 4all values of DC control signalmagnitude greater than the threshold value, the relay 22 is energizedand for all values less than the threshold value, the relay 22 is notenergized.

At time t2 the strength of the transmitted signal has decreased belowthe minimum sensitivity value but, because of the increased gainprovided by the energized relay 22, the DC control signal magnitude isstill greater than the threshold value and, consequently, the relay 22remains energized. When the transmitted signal strength decreases to thecut-off value, as shown at time t3, which value is less than the minimumsensitivity value, the DC control signal magnitude drops below thethreshold value and the relay 22 is de-energized. This results in asudden drop in the gain of the command receiver 10 and the magnitude ofthe DC control signal abruptly decreases substantially below thethreshold value, as shown by portion B2 of curve B.

Thus, chatter of the relay 22 is uniquely eliminated in applicantsimproved command receiver 10, since transmitted signal strengthvariations between the minimum sensitivity value and the cut-off value,once the minimum sensitivity value has been achieved, do not affect theenergizing or de-energizing of the relay 22.

When utilized With conventional 1l5 Ito 120 volt alternatinfg currentpower supply, the B plus voltage is applied at connection Z throughdiode and the ground is applied at Y. A transformer (not shown) ispreferably included so that approximately 6 volts may be applied at thecathode heater S2 of the tr-iode 42. Capacitors 122 and 124 lter theinput power applied to the command receiver 10 to eliminate anyalternating current therein and to eliminate any radio frequency thatmay be present in the input power supply.

When the receiver 10 is utilized to operate a relay to control theopening and closing of garage doors as described above, applicant hasfound that the components of the receiver 10 preferably have thefollowing values: Capacitor '78, 3.3 microfarads; capacitor 69, ,006microfarad; capacitor 96, 25 microfarlads; capacitor 122, 100microfarads; capacitor 124, 1000 picofarads, inductor 66 variablebetween 5 and 20 millihenries; transistors 68 and 102 'of the `2N414P-N-P type; transistors `34 and l110 of the -2N3 88 NPN type; resistor76, 1000 ohms; resistor l80, 560 ohms; resistor 92 of the thermistortype having a nominal value of 3000 ohms at 25 C.; resistor 94, 8200ohms; resistor 118, 3300 ohms; resistor 116, 27,000 ohms, and the relay22 is preferalbly a sigma No. 4l 1PP2300G type relay. Diode 120 ispreferably a Sylvania 1N462A diode.

When the receiver 10 is `fabricated including components having theabove-described values, applicant has found that the power drain in thestand-by condition is appnoximately 0.8 watt and, further, that theradiated power re-radiated from the receiving antenna 26 is virtuallyinsignificant so that spurious signals that might tend to actuatesimilar receivers in geographic juxtaposition to the receiver 10 do notoccur.

`From the above it can be seen that applicant has pro- -vided animproved selectively tuned command receiver adapted to receive tatransmitted signal comprising a radio frequency signal at a preselectedfrequency that is audio frequency amplitude modulated at a preselectedaudio frequency. Only when a transmitted signal at or above the minimumsensitivity value and having both the preselected radio frequencycomponet and the preselected audio frequency modulation component isreceived by the receiver 10 for a suiiicient length of time is the relay22 energized for appropriate operation of, for example, a garage door.Further, the receiver 10 not only uniquely eliminates, substantially,`re-radiation, but also insures that once a trans-mitted signal strongenough to initiate operation of the relay 22 is received, the relay 22will remain energized for all input signal strengths greater thanI apredetermined cut-off value and the predetermined cut-off value is lessthan the minimum sensitivity value sutiicient to initiate the energizingof the relay 22. From an examination of FIGURE 2, it can be seen thatapplicants impro-ved command receiver 10 is DC coupled between allstages, that is, there are no capacitors between stages to filter out DCcomponents of the signal.

This concludes the description of applicants improved i l receiver.Those skilled in the art may find many variations and adaptations ofapplicants invention herein and the following claims are intended tocover all such variations and adaptations falling within the true scopeand spirit of applicants invention.

I claim:

1. A command receiver of the type adapted to receive a transmittedsignal, which signal has a preselected radio frequency amplitudemodulated by a preselected audio frequency, and to energize a relay inresponse there-to comprising, in combination:

an antenna for receiving the transmitted signal;

-a radio frequency transformer having a primary winding and a secondarywinding, and said primary winding connected to said antenna;

a first detector having a first predetermined signal gain for a firstcondition of operation and a second predetermined signal gain greaterthan said first for a second condition of operation, and said firstdetector `coupled to said secondary winding of said radio frequencytransformer for receiving the transmitted signal coupled thereto by saidsecondary winding and said first detector having a cyclical frequencygenerating means for cyclically establishing therein at a predeterminedsquelch frequency rate, an oscilla'tory signal condition at saidpreselected radio frequency, modulated by said preselected audiofrequency and said preselected squelch frequency and said first detectorhaving filter means to lter said preselected radio frequency and saidsquelch frequency to provide a detected audio frequency signal at saidpreselected audio frequency;

amplification means coupled to said first detector for receiving saiddetected audio frequency signal and generating a DC control signal in aresponse thereto, said DC control signal having a magnitude proportionalto the strength of the transmitted signal received by said antenna;

a relay;

a relay driver and gain control coupled to said amplication means and tosaid relay for receiving said DC control signal and energizing saidrelay in response thereto for the condition of said DC control signalbeing present for a predetermined time interval and having a magnitudeat least as great as a predetermined threshold ualue; and

`said first condition of operation comprising said relay de-energizedand said second condition of operation comprising said relay energized,and said cyclical frequency generating means responsive to saidenergizing of said relay to provide said second predeltermined signalgain for the condition of said relay energized and to provide said firstpredetermined signal gain lfor the condition of said relay de-energized;and

said predetermined threshold value of said DC control signalcorresponding to a minimum sensitivity value of the transmitted signalfor the condition of said relay de-energized and said minimum thresholdvalue of said DC control signal corresponding to a cut-off value of thetransmitted signal, less than said minimum sensitivity value for thecondition of said relay energized.

2. The arrangement defined in claim 1 wherein said first detectorcomprises a radio frequency tank circuit resonant at said preselectedrad-io frequency, and said cyclical frequency generating means thereofcomprises a self-quenching super-regenerative detector for cyclicallyestablishing said oscillatory signal having said preselected radiofrequency at said predetermined squelch frequency rate.

3. The arrangement defined in claim 2 wherein y said radio frequencytank circuit resonant at said preselected radio frequency comprises saidsecondary winding of said radio frequency transformer and a variablecapacitor;

and said self-quenching super-regenerative detector comprises: a triodehaving a plate, a cathode and a grid, said plate connected to a firstend of said radio yfrequency tank circuit and said cathode connected toground, a capacitor having a first conductor connected to a second endopposite said first end of said radio frequency tank circuit and asecond conductor connected to said grid, a resistor connected between`said cathode and said grid; and

`signal varying means for applying a first predetermined DC voltagebetween said first end of said radio frequency tank circuit and groundto provide said first predetermined gain in said first detector for thecondition of said relay being unenergized and said predetermined DCvoltage being varied to a second predetermined DC voltage less than saidfirst predetermined DC voltage to provide said second predetermined gainin said first detector greater than said first gain for the condition ofsaid relay being energized.

4. The arrangement defined in claim 3 wherein said variable capacitor isvariable between approximately 1.5 picofarads and 9.0 picofarads to tunesaid radio frequency tank circuit for a resonance at the preselectedradio frequency in the range of 250 megacycles to 300 megacycles, saidtriode has a transconductance of approximately 4000 micromhos at a platevoltage on the order of 12 volts, and said resistor and said capacitorprovide a time constant in the range of 0.75 10-6 seconds and 2.25)Q10-6 seconds, and said first predetermined YDC voltage is in the rangeof 6 to 24 volts.

5. The arrangement defined in claim 1 wherein said preselected radiolfrequency is in the range of 250 megacycles to 300 megacycles, saidpreselected audio frequency is in the range of 12 kilocycles to 24kilocycles, said predetermined squeloh frequency is in the range of 2 to50 times as great as said preselected audio frequency and is in therange of 24 kilocycles to 1200 kilocycles, and said DC control signal isproportional to the logarithm of the strength of said transmitted signalreceived by said antenna.

6. The arrangement defined in claim 1 wherein said relay driver and gaincontrol comprises:

a relay driver transistor having base, emitter and collector electrodes,and said DC control signal is applied t'o said base electrode, and saidrelay is connected to said collector electrode and to ground;

an impedance divider transistor having base emitter and collectorelectrodes and said emitter electrode of said relay driver transistor isconnected to said emitter electrode of said impedance divider transistorto estalblish said predetermined threshold value yof said DC controlsignal for conductance of said relay driver transistor to energize saidrelay;

a first resistor connecting said base electrode of said impedancedivider transistor to ground;

a second resistor connecting said base electrode of said impedancedivider transistor to said collector electro-de of said impedancedivider transistor; and

means for applying a predetermined DC voltage between said collectorelectrode of said impedance divider transistor and ground.

7. The arrangement defined inclaim 6 wherein said y relay drivertransistor is of the P-N-P type, said impedance divider transistor is ofthe N-P-N type and said preselected DC voltage at said collectorelectrode of said impedance divider transistor is positive with respectto ground.

8. The arrangement defined in claim 6 wherein said relay drivertransistor is of the N-P-N type, said irnpedance divider transistor isof the P-N-P type and said preselected DC voltage at said collectorelectrode of 13 said impedance divider transistor is negative withrespect to ground.

9. A command receiver of the type adapted to receive a transmittedsignal, which signal has a preselected radio frequency amplitudemodulated by a preselected audio frequency, and to energize a relay inresponse thereto comprising, in combination:

an antenna for receiving the transmitted signal;

a radio frequency transformer having a primary winding and a secondarywinding and said primary winding connected to said antenna;

a first detector having a predetermined gain range and comprising aradio frequency tank circuit and a selfquenching super-regenerativedetector said radio frequency tank circuit comprising said secondarywinding of said radio frequency transformer and a variable capacitor,said self-quenching super-regenerative detector comprising a triodehaving a plate, a cathode and a grid, said plate connected to a firstend of said radio frequency tank circuit and said cathode connected toground, a first capacitor having a first conductor connected to a secondend opposite said first end of said radio frequency tank circuit and asecond conductor connected to said grid, and a first resistor connectedbetween said cathode and said grid, and means for applying a firstpredetermined DC voltage between said first end of said radio frequencytank circuit and ground, said self-quenching super-regenerative detectorfor cyclically establishing an oscillatory signal at said preselectedradio frequency at a predetermined squeich frequency rate in said firstdetector whereby a detected audio frequency signal is generated inresponse to the transmitted signal and having said preselected audiofrequency;

and filter means in said first detector for filtering said resonantradio frequency and said squelch frequency to transmit said detectedaudio frequency signal;

means coupled to said filter means for receiving said detected audiofrequency signal and generating a DC control signal in response thereto,said DC control signal having a magnitude proportional to the strengthof the transmitted signal received by said antenna;

a relay;

a relay driver and gain control coupied to said means and to said relayand comprising a relay driver transistor having base, emitter andcollector electrodes, and said DC control signal is applied to said baseelectrode, and said relay is connected to said collector electrode andto ground, an impedance divider transistor having base, emitter, andcollector electrodes and said emitter electrode of said relay drivertransistor is connected to said emitter electrode of said impedancedivider transistor to establish a predetermined threshold value of saidDC control signal for conductance of said relay driver transistor toenergize said relay, a second resistor connecting 14 said base electrodeof said impedance divider transistor to ground, a third resistorconnecting said base electrode of said impedance divider transistor tosaid collector electrode of said impedance divider transistor, means forapplying a second predetermined DC voltage different from said firstpredetermined DC voltage between said collector electrode of saidimpedance divider transistor and ground, whereby said relay is energizedfor the condition of said DC control signal having a magnitude at leastas great as said predetermined threshold value and for the condition ofsaid relay being energized, said first predetermined DC voltage isdecreased to thereby increase the gain of said first detector to providean increase in the magnitude of said DC control signal. 10. Thearrangement defined in claim 9 wherein said preselected radio frequencyis in the range of 250 megacycles to 300 megacycles, said preselectedaudio frequency is in the range of 12 kilocycles to 24 kilocycles, saidpredetermined squelch frequency is in the range of 2 to 50 times asgreat as said preselected audio frequency and is in the range of 24kilocycles to 1200 kilocycles, and said DC control signal isproportional to the logarithm of the strength of said transmitted signalreceived by said antenna, and said first predetermined DC voltage iswithin the range of 6 to 24 volts.

11. The arrangement defined in claim 1t) wherein said variable capacitoris variable between approximately 1.5 picofarads and 9.0 picofarads totune said radio frequency tank circuit for resonance at the preselectedradio frequency in the range of 250 megacycles to 300 megacycles, saidtriode has a transconductance of approximately 4000 micromhos at a platevoltage on the order of 12 volts, and said resistor and said capacitorprovide a time constant in the range of 0.75 10`6 seconds and 2.25 106seconds, said relay driver transistor is of the P-N-P type, saidimpedance divider transistor is of the N-P-N type and said secondpreselected DC voltage at said collector electrode of said impedancedivider transistor is posiytive with respect to ground, and said firstpredetermined DC Voltage is in the range of 6 to 24 volts.

References Cited UNITED STATES PATENTS 2,931,956 4/1960 Van Arsdale343-225 2,993,991 7/1961 Lundakl 343-228 3,001,177 9/1961 Adler 343-2283,041,507 6/1962 Rose et al 343-225 3,072,887 1/1963 Adler 343--2283,151,297 9/1964 Toomin 325-429 3,106,646 10/1963 Carter 317 1233,112,431 11/1963 Pederson 317-1485 THOMAS B. HABECKER, Acting PrimaryExaminer.

NEL C, READ, Examiner.

A. J. KASPER, Assistant Examiner.

1. A COMMAND RECEIVER OF THE TYPE ADAPTED TO RECEIVE A TRANSMITTEDSIGNAL, WHICH SIGNAL HAS A PRESELECTED RADIO FREQUENCY AMPLITUDEMODULATED BY A PRESELECTED AUDIO FREQUENCY, AND TO ENERGIZE A RELAY INRESPONSE THERETO COMPRISING, IN COMBINATION: AN ANTENNA FOR RECEIVINGTHE TRANSMITTED SIGNAL; A RADIO FREQUENCY TRANSFORMER HAVING A PRIMARYWINDING AND A SECONDARY WINDING, AND SAID PRIMARY WINDING CONNECTED TOSAID ANTENNA; A FIRST DETECTOR HAVING A FIRST PREDETERMINED SIGNAL GAINFOR A FIRST CONDITION OF OPERATION AND A SECOND PREDETERMINED SIGNALGAIN GREATER THAN SAID FIRST FOR A SECOND CONDITION OF OPERATION, ANDSAID FIRST DETECTOR COUPLED TO SAID SECONDARY WINDING OF SAID RADIOFREQUENCY TRANSFORMER FOR RECEIVING THE TRANSMITTED SIGNAL COUPLEDTHERETO BY SAID SECONDARY WINDING AND SAID FIRST DETECTOR HAVING ACYCLICAL FREQUENCY GENERATING MEANS FOR CYCLICALLY ESTABLISHING THEREINAT A PREDETERMINED SQUELCH FREQUENCY RATE, AN OSCILLATORY SIGNALCONDITION AT SAID PRESELECTED RADIO FREQUENCY, MODULATED BY SAIDPRESELECTED AUDIO FREQUENCY AND SAID PRESELECTED SQUELCH FREQUENCY ANDSAID FIRST DETECTOR HAVING FILTER MEANS TO FILTER SAID PRESELECTED RADIOFREQUENCY AND SAID SQUELCH FREQUENCY TO PROVIDE A DETECTED AUDIOFREQUENCY SIGNAL AT SAID PRESELECTED AUDIO FREQUENCY; AMPLIFICATIONMEANS COUPLED TO SAID FIRST DETECTOR FOR RECEIVING SAID DETECTED AUDIOFREQUENCY SIGNAL AND GENERATING A DC CONTROL SIGNAL IN A RESPONSETHERETO, SAID DC CONTROL SIGNAL HAVING A MAGNITUDE PROPORTIONAL TO THESTRENGTH OF THE TRANSMITTED SIGNAL RECEIVED BY SAID ANTENNA; A RELAY; ARELAY DRIVER AND GAIN CONTROL COUPLED TO SAID AMPLIFICATION MEANS AND TOSAID RELAY FOR RECEIVING SAID DC CONTROL SIGNAL AND ENERGIZING SAIDRELAY IN RESPONSE THERETO FOR THE CONDITION OF SAID DC CONTROL SIGNALBEING PRESENT FOR A PREDETERMINED TIME INTERVAL AND HAVING A MAGNITUDEAT LEAST AS GREAT AS A PREDETERMINED THRESHOLD VALUE; AND SAID FIRSTCONDITION OF OPERATION COMPRISING SAID RELAY DE-ENERGIZED AND SAIDSECOND CONDITION OF OPERATION COMPRISING SAID RELAY ENERGIZED, AND SAIDCYCLICAL FREQUENCY GENERATING MEANS RESPONSIVE TO SAID ENERGIZING OFSAID RELAY TO PROVIDE SAID SECOND PREDETERMINED SIGNAL GAIN FOR THECONDITION OF SAID RELAY ENERGIZED AND TO PROVIDE SAID FIRSTPREDETERMINED SIGNAL GAIN FOR THE CONDITION OF SAID RELAY DE-ENERGIZED;AND SAID PREDETERMINED THRESHOLD VALUE OF SAID DC CONTROL SIGNALCORRESPONDING TO A MINIMUM SENSITIVITY VALUE OF THE TRANSMITTED SIGNALFOR THE CONDITION OF SAID RELAY DE-ENERGIZED AND SAID MINIMUM THRESHOLDVALUE OF SAID DC CONTROL SIGNAL CORRESPONDING TO A CUT-OFF VALUE OF THETRANSMITTED SIGNAL, LESS THAN SAID MINIMUM SENSITIVITY VALUE FOR THECONDITION OF SAID RELAY ENERGIZED.